A stereo image processing apparatus that measures a distance to a photographing object by performing stereo measurement is already known (for example, see Patent Literature 1). According to the conventional stereo image processing apparatus, a distance to a photographing object is calculated using two camera images that are photographed using two cameras. The two camera images can also be said to be images for distance measurement. Further, according to the conventional stereo image processing apparatus, one of the two camera images (images for distance measurement) is used as a monitoring image.
However, according to the conventional image processing apparatus, since only one of the two camera images (images for distance measurement) is utilized as a monitoring image, the signal-to-noise ratio (S/N ratio) of the video signal is low. Non-linear processing such as gamma correction processing is performed on a video signal to be used for a monitoring image, and the amplitude of a low- or medium-brightness video signal is expanded. However, at such time, if the S/N ratio of the video signal is low, the non-linear processing causes an increase in the amount of noise, and the image quality of the monitoring image deteriorates as a result.